1. Field of the Invention
This invention relates to a beam splitter for color imaging apparatus, and more particularly, to a beam splitter which is particularly suitable for use in a linear array film scanner.
2. Description of the Prior Art
A linear array film scanner for use in television applications typically includes a light-sensitive linear charge coupled device (CCD) which provides a serial output representing a line of a television raster. For color television, the film scanner can include an assembly of three separate CCD arrays, one for each of the primary colors. The film is driven at a uniform rate past a light source, and a lens and beam splitter image an illuminated section of the film onto each CCD array. The film motion provides the vertical (frame) scan, and the linear cycling of the CCD arrays provides the horizontal (line) scan. Such a scanner is described in U.S. Pat. No. 4,205,337.
It is also known in film scanning systems to use a beam splitter to divide light from an illuminated line of film into two images, a luminance image and a chrominance image. A system of this type is shown, for example, in U.S. Pat. No. 4,310,847. One of the problems in a two-channel system is in achieving the proper color balance in each of the detection channels. In order to achieve the desired weighting of the primary colors in the luminance channel of the patented device, a color filter is placed in the channel to enhance or suppress portions of the visible spectrum. A repetitive array of color filters are also placed in the path of the chrominance image. The use of the separate balancing obtain in the system to obtain the desired color balance, however, makes the system considerably more complex. A further drawback is that the various filters tend to change in effectiveness over time, and thus, it is difficult to maintain the system in calibration.